N-formylglycine was developed as a dead-end inhibitor of the succinic semialdehyde dehydrogenase reaction. At 4mM, it inhibited Aspergillus niger succinic semialdehyde dehydrogenase by 40%. N-formylglycine is a reversible, complete inhibitor; the inhibition is competitive with succinic semialdehyde and uncompetitive with respect to NAD(+) and the K-i values are 4.9 and 10.4 mM respectively. Potato succinic semialdehyde dehydrogenase is also inhibited by N-formylglycine to a similar extent, the nature of the inhibition being identical to that observed with the A. niger enzyme.